1. Field of the Invention
The present invention relates to a recording apparatus for making a record by the use of a recording head.
2. Description of the Related Art
Hitherto, a thermal-type inkjet recording apparatus makes a record by applying pulse voltage to a heat-generating resistor (heater resistance), and discharging ink from an ink discharging port by boiling ink in an ink chamber located adjacent to the heater resistance instantaneously and causing babble expansion to be generated. Therefore, drive energy required for discharging a fixed amount of ink varies with the temperature of the ink or the temperature of the recording head. In contrast, when a fixed amount of drive energy is always supplied to the heater resistance, the temperature of the recording head increases due to variations in environmental temperature or continuous usage, which causes variations in the amount of ink discharge and hence density or color tone of the image to be recorded varies, thereby deteriorating the quality of the image.
In order to avoid such deterioration of image quality, a method of providing a temperature detecting element in a semiconductor device 52 (hereinafter referred to as a “heater board”) of a recording head 50 as shown in FIG. 9, detecting the temperature of the recording head, and adjusting the pulse width of the drive pulse according to the detected temperature. The adjusting unit has substantially a structure as described below. The temperature detecting element provided on the recording head is, for example, a diode 57, and the amount of variation of forward voltage VF in association with the temperature is detected by entering the forward voltage VF generated when constant current is flowing through the diode into an A/C converter 13, and converting the entered value to the digital amount. The detected temperature is divided into about four stages by every 10 to 15° C. within the allowable temperature range of the recording head. Variations in the amount of ink discharge with the temperature are restrained by switching the pulse width table of drive pulse signals for driving the heater resistance within this temperature range.
When the temperature of the recording head is low (0° C. to 15° C.), since the viscosity of ink is high, there may be the case in which double pulse drive combined with pre-pulse for preparatory heating is performed in order to secure a predetermined amount of ink discharge. In this manner, recording action is performed by controlling the pulse width by the temperature of the recording head. For example, control to differentiate the pulse width of the drive pulse in accordance with the temperature as shown in Table 1 provided below.
However, in the recording apparatus described above and control thereof, there are problems as listed below:    (1) An AD converter for converting the temperature data of the recording head to the digital amount is necessary, and complex control including the steps of detecting variations in temperature at certain intervals by a controller provided on the main body of the recording apparatus and switching the drive pulse table is necessary. Resolution of the detected temperature is, for example, about four stages in order to curb product costs. Therefore, at the moment when the drive pulse is switched in the course of changing the temperature of the recording head, drive energy applied to a heater resistance 54 varies discontinuously, thereby causing fluctuation in the amount of ink discharge.    (2) In association with advances in velocity and fineness of the recording apparatus, an increase in the number of recording head nozzles and in discharging frequency is required. Therefore, in order to compensate variations in manufacture of heater boards or in order to compensate drive energy in association with the above described variations in temperature, constraints in the pulse width which is changeable in one drive pulse is resulted. In particular, since the necessary length of the pulse width for discharging ink gets longer with lower temperature, change in the pulse width of the double pulse used as the drive pulse is more difficult at low temperature.